This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Oligosaccharides are biopolymers composed of multiple monosaccharide units connected through glycosidic bonds. Structural characterization of oligosaccharides requires not only determination of the identity and sequence of each monosaccharide unit, but also differentiation of possible branching, linkage, epimeric and anomeric isomers. It has been shown previously, in our lab and elsewhere, that electron capture dissociation (ECD) and hotECD (hECD) generally provide more extensive cross-ring cleavages than the conventional collisionally activated dissociation (CAD) and infrared multiphoton dissociation (IRMPD) methods. These cross-ring fragments are instrumental in determining the branching and linkage sites. In this study, metal-adducted permethylated linear and branched oligosaccharide ions were subject to ECD at several energies to investigate the effect of metal ion and electron energy on their fragmentation behaviors as well as the general applicability of ECD to isomer differentiation.